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Is it possible to use multiple tor circuits chained together?

tor_circuit --> tor_circuit --> ... --> tor_circuit

I know of a solution on windows using tortilla for windows that allows forwarding all traffic on a workstation through tor. Consequently, using a virtual machine in conjunction with tor allows for a tor chain of length 2:

tor_circuit --> tor_circuit

I know that a tor circuit can use a predefined number of nodes

entry --> relay --> ... --> relay --> exit 

but in this instance the connection has the same id over the whole chain which can be identified by an attacker controlling a number of the respective nodes.

Using new chains, chained together would prevent that. But how can it be done?

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I read this document which says it is possible to use a transparent proxy to create what they call a "Tor over Tor scenario" (or a chain of two tor circuits). It is however not recommended because they say "It is not clear if this is safe"

When using a transparent proxy, it is possible to start a Tor session from the client as well as from the transparent proxy, creating a "Tor over Tor" scenario. Doing so produces undefined and potentially unsafe behavior. In theory, however, you can get six hops instead of three, but it is not guaranteed that you'll get three different hops - you could end up with the same hops, maybe in reverse or mixed order. It is not clear if this is safe. It has never been discussed.

If I understand correctly this is the possible solution you are describing with tortilla and the document shows you are right. However as you can see the circuits don't seem to work in the expected way and not enough research is being done to find out how this effects anonymity.

  • It's not just that it's unclear if it's safe... it will actually fully deanonymize you after a certain amount of time as soon as you end up using the same relay as both the guard for the first Tor and the exit for the final Tor. This issue is prevented when using only one Tor process because it is smart enough not to assign the roles of the guard and exit to the same relay. – forest May 5 '18 at 23:15

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